Dying stars could make frozen planets habitable

[Menydh]

Dying stars could make frozen planets habitable

New Scientist
March 29, 2005

Planet hunters should look for potential havens for life around dying stars, suggest new calculations.

Astronomers think the best environment for life around any star lies in a "habitable zone" – the zone in which a planet's surface temperature means liquid water can exist. Previous work has shown this belt widens and expands outward as stars like the Sun heat up and become bloated with age.

Now, a trio of astronomers in France and the US has calculated how long the habitable zone remains at various distances from the star. They compared that with the time it took for life to emerge on Earth - an estimated 700 million years - to see if the expanding "heat wave" could kick-start life on once-frozen planets.

They found stars like our Sun go through three stages that could foster life. The first lasts for about 10 billion years while the star burns hydrogen in its core. Our Sun is currently in such a period, called the "main sequence", and the Earth lies within this stage’s habitable zone. The zone extends from just within Earth's orbit to nearly the orbit of Mars (or 0.95 to 1.37 astronomical units, with 1 AU being the distance between the Earth and Sun).

Growing core

Then, when the star begins to burn its hydrogen in a shell around a growing helium core, it brightens and expands and becomes a "sub-giant". The habitable zone sweeps outward, extending from 2 to 9 AU. The inner edge of this zone remains habitable for several billion years while the outer extreme, where Saturn currently orbits, is habitable for a few hundred million years.

The star then fluctuates in brightness for about 20 million years as it switches to burning helium almost exclusively, before becoming a red giant and swelling to 10 times the diameter of the Sun. For about a billion years afterwards, the habitable zone around the red giant extends from 7 to 22 AU, the outer edge of which lies beyond the orbit of Uranus.

"So planets that are currently very cold and icy can warm up and become potentially habitable," says William Danchi, a team member and astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The analysis shows the time period over which these conditions change is very long - long enough for life to form."

This work suggests "micro-organisms could be transported [via meteorites] from a planet where life is ending to a planet where favourable conditions for its re-birth are encountered," write the authors in a study to be published in July in the Astrophysical Journal.

Expanded horizons

Nearly 150 sub-giant and red giant stars lie within about 100 light-years of Earth, compared to about 1000 main sequence stars. Future searches for life-bearing planets, such as NASA's Terrestrial Planet Finder (TPF) space mission, will focus on the main sequence stars.

But Danchi and colleagues Bruno Lopez and Jean Schneider in France argue they should also target the dying giants. The more distant habitable zones around these giants will make the planets easier to resolve in the glare of the parent stars, they argue.

"It's a very interesting idea and we probably should expand our horizons in thinking about what kind of stars we want to look at," says Wesley Traub, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. He will soon become project scientist for the TPF space telescope, which will block the light from stars about the size of the Sun to image their orbiting planets.

He says one technical hurdle in including the dying giants in the TPF survey may arise if "the star is so wide it peeks out from behind this elaborately designed mask we've built to hide the star", he told New Scientist.



[source]

[Timo]

However, this leaves little time for evolution to take place. If the planet is only able to support life, after this stage takes place. I also think it is irrational to believe that micro-organism can't evlove in icy environments. Also, as for habbitation (by Earth-based life anyway), dying stars give off a heck of alot of radiation, depending on composition and mass.

[Xenophon]

If the purpose of searching for other planets is to find out if there is life, then I suggest to all readers of this thought the following proposition:


1. Overcome the Technological barriers associated with the ability to identify such planets

&

2. Overcome the bureaucracy associated with the announcement of existing life.

Which one of the two do you think is harder to overcome?

[Blood Axis]

Originally Posted by Xenophon

If the purpose of searching for other planets is to find out if there is life, then I suggest to all readers of this thought the following proposition:


1. Overcome the Technological barriers associated with the ability to identify such planets

&

2. Overcome the bureaucracy associated with the announcement of existing life.

Which one of the two do you think is harder to overcome?

No 2